I need to have a views handler for Views Search API that will allows empty (i.e. NULL) values in fields to be sorted last. For the simple views there is a solution: Views Sort Null Field but I'm totally lost, How to implement the same functionality for Views Search API?
More specifically - Views Search API provide only
$query->sort() method that not allow you to add sort formula like
$this->query->add_orderby(NULL, "ISNULL($this->table_alias.$this->real_field)", $this->options['order'], $alias)